INTRODUCTION

Because of its enormous sensitivity and imaging capabilities, the ALMA will be the premier instrument at millimeter and submillimeter wavelengths. Polarization observations will likely be carried out far more frequently with the ALMA than with present telescopes because the sensitivity of the ALMA will make such observations (which always have to deal with signals only a few percent of the total intensity) possible for a much larger set of radio sources. However, polarization observations place significantly more stringent requirements on instruments than do total intensity measurements. Careful consideration of the instrumental requirements for successful polarization observations should therefore be given high priority in the design of the ALMA.